Lithium Metal Graphic
Top row: top view and cross sections of deposited lithium at 70 kPa. Bottom row: top view and cross sections of deposited lithium at 350 kPa. The higher pressure causes the lithium particles to deposit in neatly stacked columns, which increases the volume of lithium deposited and prevents porosity.

A team of materials scientists and chemists has determined the proper stack pressure that lithium metal batteries, or LMBs, need to be subjected to during battery operation in order to produce optimal performance. The team includes researchers from the University of California San Diego, Michigan State University, Idaho National Laboratory, and the General Motors Research and Development Center.

Using lithium metal to replace the graphite for battery anodes is the ultimate goal for part of the battery R&D field; these lithium-metal batteries (LMBs) have the potential to double the capacity of today’s best lithium-ion technologies. For example, lithium metal battery-powered electric vehicles would have twice the range of lithium-ion battery-powered vehicles, for the same battery weight.

Despite this advantage over lithium-ion batteries, LMBs are not considered a viable option to power electric vehicles or electronics, because of their short lifespan and potential safety hazards, specifically short circuits caused by lithium dendrite growth. Researchers and technologists had noticed that subjecting LMBs to pressure during battery cycling increases performance and stability, helping to solve this lifespan challenge. But the reasons behind this were not fully understood.

The researchers used several characterizations and imaging techniques to study LMB morphology and quantify performance when the batteries were subjected to different pressures. They found that higher pressure levels force lithium particles to deposit in neat columns, without any porous spaces in between. The pressure required to achieve this result is 350 kilo Pascals (roughly 3.5 atmospheres). By contrast, batteries subjected to lower levels of pressure are porous and lithium particles deposit in a disorderly fashion, leaving room for dendrites to grow. They also showed that the process doesn’t affect the solid electrolyte interphase (SEI) structure of the batteries’ electrolytes.

Another way to boost performance is to not completely discharge the battery while it cycles. Instead, the researchers keep a reservoir of lithium where re-nucleation can occur. These findings were validated at the General Motors Research and Development Center in Michigan.

Separately, researchers at Idaho National Laboratory used molecular dynamics simulations to understand the stack pressure range used in this work, which is much less than that expected based on macroscopic mechanical models.